Romidepsin and plitidepsin share a rare chemical lineage. Both are depsipeptides — peptide chains in which one or more amide bonds are replaced by ester bonds — and both originate in marine organisms rather than in mammalian biology. They are the clearest example of natural-product peptide chemistry reaching the clinic, and of the gap between US, Australian and European regulatory outcomes.
Mechanisms differ. Romidepsin, derived from Chromobacterium violaceum, is a bicyclic depsipeptide that inhibits histone deacetylases (HDACs), shifting the gene-expression programme that governs cell proliferation and death. Plitidepsin, isolated from the ascidian Aplidium albicans, binds elongation factor eEF1A2 and acts through a non-canonical route to induce apoptosis. One class of molecule, two distinct targets.
Regulatory picture. Neither compound holds a UK marketing authorisation, and neither was authorised in the EU. The EMA refused marketing authorisation for Istodax (romidepsin) in 2012 for peripheral T-cell lymphoma, confirming that refusal on re-examination. PharmaMar withdrew its Aplidin (plitidepsin) application on 23 July 2025 during re-examination, after the EMA had recommended refusal for multiple myeloma. Romidepsin is approved in the US for cutaneous T-cell lymphoma, and its US peripheral T-cell lymphoma indication was withdrawn in 2021 under accelerated-approval rules. Plitidepsin was approved in Australia. The peptide field's most-cited 'licensed' oncology members are, in several important jurisdictions, licensed elsewhere — and not here.
For UK readers the framing matters. A US or Australian authorisation is not an MHRA licence, and what may lawfully be supplied in the UK is governed by the Medicines Act 1968, the Human Medicines Regulations 2012 and, where relevant, the Misuse of Drugs Act 1971. Both compounds sit outside licensed UK use. Describing either as a UK-licensed medicine would be inaccurate; treating the whole group as unlicensed would equally flatten a genuinely instructive split.
Research use only. Nothing here is consumption or dosing guidance.
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.